1. Technical Field
This application relates to computer storage devices, and more particularly to the field of transferring data between storage devices.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
In some cases, different users or groups of users that share a storage device are independent of each other. For example, different companies and/or different departments in the same company and/or different applications or groups of applications may share a storage device. When this occurs, it is often useful to be able to allocate storage device resources in a way that provides sufficient response time to all of the independent users. Such allocation may be informal or may be provided formally in a service level agreement or similar. However, providing a guaranteed level of service in an efficient manner may be difficult, especially in situations where the configuration and load levels of different users change often.
Accordingly, it is desirable to have different entities using a storage system be provided with a guaranteed level of service in an efficient and reliable manner.